This invention relates to television camera systems for insuring the registration of the amplitude of video signals developed by multiple image pickup devices in a television camera.
In a multiple image pickup television camera, such as a modern color camera, it is necessary to insure that the television raster developed in conjunction with each image pickup device is in registration and further necessary to insure that the amplitude of the video signal developed by each image pickup device, for example, the red, green, and blue color images, are substantially the same amplitude at both the black level (absence of light) and the white level, which represents full illumination and equal amounts of red, green, and blue color signals. Automatic gain control (AGC) circuits are known, in which the video signal amplitudes are compared with a given reference in a comparator circuit to develop a control signal which is, in turn, coupled back to a gain control device for adjusting the amplitudes of the video signals. However, these known circuits are generally analog in nature, whereas the more modern trend in television camera systems is to provide digital control of all such automatic functions. It is desirable, therefore, to develop the required control signals inexpensively and directly in digital form so that they may be processed with known digital control systems, such as microprocessor control systems.